Buggy code:
@ Mapper ( uses = { ModelMapper . ModelMapper . class , ParameterMapper . class , SecurityMapper . class } ) public abstract class ServiceModelToSwagger2Mapper { @ Mappings ( { @ Mapping ( target = "swagger" , ignore = true ) , @ Mapping ( target = "info" , source = "resourceListing.info" ) , @ Mapping ( target = "paths" , source = "apiListings" ) , @ Mapping ( target = "basePath" , expression = "java(anyApi(from).getBasePath())" ) , @ Mapping ( target = "host" , expression = "java(anyApi(from).getBasePath())" ) , @ Mapping ( target = "schemes" , expression = "java(toSchemes(anyApi(from)))" ) , @ Mapping ( target = "produces" , expression = "java(anyApi(from).getProduces())" ) , @ Mapping ( target = "consumes" , expression = "java(anyApi(from).getConsumes())" ) , @ Mapping ( target = "parameters" , expression = "java(new<seq2seq4repair_space>java.util.HashMap())" ) , @ Mapping ( target = "definitions" , expression = "java(modelMapper.mapModels(allApiModels(from)))" ) , @ Mapping ( target = "securityDefinitions" , expression = "java(securityMapper.toSecuritySchemeDefinitions(anyApi(from)))" ) , @ Mapping ( target = "externalDocs" , ignore = true ) } ) public abstract Swagger map ( Group from ) { } @ Mappings ( { @ Mapping ( target = "license" , expression = "java(toLicense(from))" ) , @ Mapping ( target = "contact" , expression = "java(toContact(from))" ) , @ Mapping ( target = "termsOfService" , source = "termsOfServiceUrl" ) , @ Mapping ( target = "vendorExtensions" , ignore = true ) } ) protected abstract Info map ( ApiInfo from ) { } @ Mappings ( { @ Mapping ( target = "description" , source = "notes" ) , @ Mapping ( target = "operationId" , source = "nickname" ) , @ Mapping ( target = "schemes" , source = "protocol" ) , @ Mapping ( target = "produces" , source = "produces" ) , @ Mapping ( target = "consumes" , source = "consumes" ) , @ Mapping ( target = "parameters" , source = "parameters" ) , @ Mapping ( target = "security" , source = "authorizations" ) , @ Mapping ( target = "responses" , source = "responseMessages" ) , @ Mapping ( target = "tags" , ignore = true ) , @ Mapping ( target = "vendorExtensions" , ignore = true ) , @ Mapping ( target = "externalDocs" , ignore = true ) } ) protected abstract Operation map ( com . mangofactory . documentation . service . Operation from ) { } protected License toLicense ( ApiInfo from ) { } protected List < Scheme > toSchemes ( ApiListing from ) { } protected Contact toContact ( ApiInfo from ) { } protected List < Map < String , List < String > > > map ( Map < String , List < AuthorizationScope > > from ) { } protected Function < AuthorizationScope , String > scopeToString ( ) { } protected static Map < String , Response > map ( Set < ResponseMessage > from ) { } protected Map < String , Path > mapPaths ( Map < String , ApiListing > apiListings ) { } protected Path map ( ApiDescription api ) { Path path = new Path ( ) ; for ( com . mangofactory . documentation . service . Operation each : api . getOperations ( ) ) { Operation operation = map ( each ) ; <START_BUG> path . set ( each . getMethod ( ) , operation ) ; <END_BUG> } return path ; } protected Map < String , Model > allApiModels ( Group group ) { } protected ApiListing anyApi ( Group group ) { } private Function < String , Scheme > toScheme ( ) { } }

Fix:
path . set ( each . getMethod ( ) . toLowerCase ( ) , operation ) ;